Great masks. Assuming that they hold up to the quality defined by KF-94, then they’re great extra protection for COVID as well, and should be superior to a standard surgical mask. I am not a doctor or a professional so I can’t promise and have not tested them, just going by the standard they should be very good.
The best part is the seal. The bottom fold design makes it seal against the chin much better than standard masks, and if you twist the ear straps the sides seal very well as well. I can’t detect any leakage and it feels like all air is going through the filter.